Please explain the single-mic technique of sound reinforcement (5 questions and replies)

What are the preferred mics for the single-mic technique of sound reinforcement? I have seen two mics used about five feet apart center stage at larger festivals.
Phil 


Reply: Please see this article:  single-mic technique.htm

 

The Crown CM-700 cardioid condenser would work well for this application because it has low noise and very little off-axis coloration.


With large groups, one mic can't always pick up everyone effectively because some players will be too far from the mic. In this case the group uses two mics, each picking up half the group. Sometimes an extra pickup or mini mic (GLM-100) will be needed on certain instruments.

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I really enjoyed your article on the single microphone technique, as we have seen quite a number of groups, mainly bluegrass, using this technique and we have had really good success with it in smaller, more intimate settings. Single-mic technique article

However, at our most recent show the single mic technique proved not quite as ideal. The venue was a family concert series in an outdoor park, amphitheater type setting with an audience of approx. 2000 - 2500, who chose to talk through the vast majority of the band's performance. The sound system itself has more than enough power for the venue as we have used the same system for blues, pop, jazz, etc. in the same setting. The 4-piece bluegrass band brought their own main microphone and wanted an additional mic for the acoustic guitar and had a mic strapped to the stand up bass. The group did an excellent job at working the mic during their performance, most of the time huddling within a foot of the mic. 


That said, we spent the entire evening riding the gain, just shy of feedback, trying to keep the band above the crowd noise toward the back half of the park. In between songs, the band's announcements and lead-ins were all but completely lost as the band was more soft-spoken when not singing. And of course we had EQ'd things out as far as we could stretch that, too. The mic was so hot that, in between songs, you could literally hear the kids playing on the hillside directly behind the stage, separated by a concrete wall. Yet, there didn't seem to be enough level to keep the group on top of the audience noise. The sound we had was at least fairly full and not thin as can be typical with this mic technique.


What would have worked better? Do you have any recommendations? Any input would be great as bluegrass groups are quite prevalent in this area.
Ken Jacobs
Jacobs Productions - Pro Audio & Lighting

Reply: As your situation shows, it's hard to determine during the sound check (if any) whether the single mic will work, because the audience noise can be such a factor.

Be sure the floor monitors are off. They are usually the main source of feedback.

Compared to a cardioid mic, a supercardioid or hypercardioid mic would tend to have less feedback, but they also have tighter polar patterns - requiring all the band members to stay in front of the mic, which is difficult or impossible. So you might use two mics about 5 feet apart so that the band members can get a little closer to the mics. They would have to re-learn their mic technique, though. You might try a bidirectional mic with its side nulls aiming at the left and right house speakers.

Before the show, maybe you could say to the band members: "In this venue, some bands can't be heard loud enough with a single mic. So please play loudly and yell the announcements. Otherwise the audience may not be able to hear you. I'll cup my ears as a signal for you to talk louder if I can't hear you".

Another option: Set up your usual group of multiple mics, and put the single mic downstage from those mics. Before the show, you might say to the musicians, "Use your single mic first, and we'll try that. If it isn't loud enough, I'll signal you to go to the other mics. Those extra mics will be hidden just behind the group until the mics are used." This changeover can be awkward, but it might be your only option.
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We are a three-piece acoustic band: one guitar, fiddle or dobro, mandolin and two vocals. We own a 100-watt acoustic combo amp with an open back. We want to try feeding it with a single condenser mic. Do we have a chance with this technique in a small room without feedback problems?
Jeremy Carrivick

Reply: The single-mic technique should work in a small room if you take some precautions. If you can, place the combo amp far from the mic and close to the audience, so that the speakers are on the "dead" back side of the mic's cardioid polar pattern. Try to sing and play as close to the mic as possible. Don't use any monitor speakers. In-ear monitors work great.

Try out this system and see if it has enough gain before feedback in your venue. If not, use a 1/3rd octave graphic EQ to turn down frequencies that feed back. The graphic equalizer connects between your mixer output and power amp input, if that is possible with your equipment. Maybe your mixer-amp has a graphic equalizer built in.

Before the audience arrives, slowly turn up the mic volume until you hear a feedback tone. Find the frequency on the graphic equalizer that stops the feedback when you push down the frequency slider. Push it down just to the point where feedback stops. Then turn up the mic volume until feedback occurs again (usually at another frequency). Find the right frequency, turn it down, and repeat for about 4 or 5 frequencies. The system should be louder without feedback than it was before using the equalizer.

You could use an automatic feedback exterminator (like Sabine or Shure) instead.

Here's a weird idea. The sound from the front of the open combo amp is out of phase with the sound from the back of the open combo amp. So maybe if you put the combo amp to the SIDE of the mic, facing the audience, the front and back sounds will cancel out at the mic, giving you more gain before feedback.

Also, you may need to place the combo amp on a stand, chair or box to make it high enough to project sound over the heads of the first row of the audience. Otherwise the audience members will block the sound from reaching the back row of the audience.

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I play in a bluegrass gospel group. What is the best way to EQ or set the sound for a single mic set up? The problem we have is getting the mic and the house sound loud enough without getting feedback. Could you please give me some tips on how to start from square 1 to set the EQ and get the mic as hot as possible as well as the house level?
Jason Burton
The Bluegrass Gospel Reflections

Reply: With the single-mic technique, it is difficult to get enough volume without feedback because the microphone is far from the performers. If your group has more than two or three people, you might want to use a second microphone (one mic on every two or three people) so that the performers can get closer to the mics. Also, do not use monitor speakers. Either listen to each other live on stage, or use in-ear monitors.

SETTING GAIN STAGING
1. Connect a 1/3-octave graphic equalizer between the mixer output and the house power-amp input. Set the equalizer controls to flat and 0 dB gain (unity gain). Turn on the equalizer.
2. On the mixer, assign the mic channel to the master output bus (channel 1 and 2 out, or whatever it's called.)
3. Turn down the mixer's master fader, mic fader, and mic channel input trim (gain or atten). Turn down the power amp levels to minimum.
4. Have the band play a loud song. Gradually turn up the mic channel's trim knob just to the point where the clip light comes on, then turn down the trim knob about 10 dB so you have some headroom. You won't hear any sound at this point.
5. Set the master fader to 0 (the shaded portion of fader travel, about 3/4 up).
6. As the band is playing, turn up the mic's fader until the mixer level meters peak near 0 maximum. Note where the mic's fader level is, then turn it down 12 dB from that point. You won't hear any sound yet.
7. Gradually turn up the power-amp volume; you'll hear the amplified band through the house PA speakers.

REDUCING FEEDBACK
The basic procedure: To reduce feeback, you will slowly turn up the mic volume until feedback starts, then use the graphic equalizer to cut the frequency that is feeding back, and repeat those two steps several times.

1. Ask the band to stop playing. Keep turning up the power-amp volume just until you start to hear feedback ringing at a single frequency. The band should plug their ears or wear ear plugs to avoid ear damage from feedback.
2. Turn down each slider on the graphic equalizer, one at a time, until you find the slider that stops the feedback tone. Set that slider to zero, then reduce its level until feedback stops.
3. Gradually bring up the mic's fader until you start to hear feedback ringing at a single frequency. It might be a different frequency than the first time.
4. Repeat steps 2 and 3 four or five times.
5. Turn down the mic fader a little until feedback and ringing stop. Ask the band to play. The sound should be louder without feedback than when you started.

Some bands use an automatic feedback suppressor such as made by Sabine or Shure.

Good luck; it's a challenge to make this technique work.

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I have a question about using single microphones for a bluegrass band. I first saw it done effectively with Allison Krauss about five years ago; they each stood about 8 feet from it, and stepped a couple of feet closer to solo. Excellent sound! When, soon after, I saw Del McCoury using this system, I was under the impression that they stood closer, and that the balance was a bit less regular. . . but still quite fine.

I now find myself playing bass in a six-piece bluegrass band. One member has a cardioid condenser mike, which sounds very good in a relaxed stage configuration. But as the evening progresses, the solo instrumentalists or lead vocalists "crowd" the mike, standing maybe a foot away, and blocking its pickup of instruments behind the soloist. So, many other instruments fall from the mix, and we can't really hear each other, except with floor monitors. No amount of microphone choreography seems to solve the problem.

How far from the mike should all musicians stand? How close should soloists appoach?
Rees Chapman

Reply: A six-piece band probably would need to use two microphones (three musicians on each mic). That way, nobody gets blocked, and more people can get close to their mic. Follow the 3-to-1 rule: the mics should be spaced apart at least 3 times the mic-to-source distance. Six-foot spacing is typical.

You need to stand as close to the mics as physically possible without crowding each other. That way, the mic picks up a loud signal, so the sound mixer doesn't have to turn up the mic so much and cause feedback.

The soloist should stand in front of the mic about a foot away. It really helps to practice while listening to the PA. Run the mics through a PA system with the speakers aimed at the musicians. Practice moving in and out while listening to the balance. Pretty soon you'll know by ear where to stand.

With the 1-mic or 2-mic technique, it's hard to get enough gain-before-feedback in noisy venues because the performers are much farther from the mics than in a multi-mic setup. Some performers have to omit the stage monitors (to prevent feedback) and just listen to each other live on stage.

One bluegrass/old-time band, Uncle Earl, uses the 2-mic technique augmented by spot mics. They use the two large condenser mics for the vocals and fiddle, and use clip-on mics or pickups for the instruments that need it.